This invention relates to an apparatus for removing adhered slag or other foreign materials that adhere to the refractory material forming a soaking hearth in a reheat furnace for metallic workpieces, and more particularly, the present invention provides an apparatus for removing adhered slag and the like from a furnace hearth during operation of the furnace by providing a car adapted to move along the floor at a side wall of the furnace while carrying a digging bar that is coupled to a pneumatic hammer or the like for delivering a digging force to the bar while it extends through an opening in the side wall of the furnace to engage and lossen adhered slag on the hearth.
Reheating furnaces are commonly employed to heat billets, blooms, slabs and similar workpieces to temperatures up to 2400.degree. F. Furnaces built generally before 1950 were designed with refractory hearths that were up to 25 feet wide, however since that time, the width of the workpiece supporting hearths has been increased up to about 42 feet maximum. The metallic workpieces are advanced through the furnace in a side-by-side relation either by a pusher at one end of the furnace or by means of walking beams within the furnace.
In present-day reheat furnaces, the workpieces enter through a charging door at one end of the furnace and first pass into a preheat zone from where the workpieces are advanced into a heating zone. Frequently, the outer surfaces of the workpieces become overheated or "superheated" in the heating zone before they are advanced into a soaking zone where a solid hearth made of refractory material provides continuous support for the workpieces. As the workpieces enter the soaking zone of the furnace, the superheated state of the adhered slag which includes scale and the like is semiplastic. The slag is transferred from the bottom surface of the workpiece to the hearth. The released slag from the workpiece solidifies and accumulates because the hearth is usually relatively cooler than the surface temperature of the workpiece when it enters the soaking zone. As the workpieces pass from the soaking zone they usually travel along a downwardly-inclined discharge chute and pass from an opening normally closed by a discharge door onto a roller table for conveying the workpiece to the rolling mill or the like. Some present-day reheat furnaces require a mechanical extractor to lift and remove a heated workpiece from the soaking zone and deposit it upon a roller table.
Prior to the time when the workpiece leaves the soaking zone, there is a tendency for scale and slag to be again transferred from the heated workpiece onto the hearth. The build-up of slag at the point where the workpieces enter the soaking zone and exit from the soaking zone creates acute operational problems in regard to irregular or unpredictable movements of the workpieces. If slag is allowed to accumulate on the hearth at the point where a workpiece enters the soaking zone, the forward edge of the workpiece is lifted and may be deflected upwardly. When this occurs, the workpiece is either pushed on top of the workpiece ahead of it or the workpiece rotates and stands on its side edge. In either event, the soak zone roof or drop-out area of the furnace is usually damaged. Repairs are costly and very time-consuming because operation of the furnace must be discontinued. A workpiece has actually penetrated through the furnace roof due to accumulated slag. The "soak zone nose" is that part of the furnace roof that forms a narrow entranceway into the soaking zone.
A water-cooled lintel as well as a furnace door located below it in the end wall of the furnace are particularly susceptible to damage when a workpiece fails to properly enter onto the downwardly-inclined skids at the discharge side of the soaking zone. Damage to the furnace, particularly the lintel, frequently occurs when two workpieces slide down the skids one on top of the other which is a condition caused by adhered slag on the hearth of the entrance to the soaking zone. Erratic movements of the workpieces at the discharge side of the soaking zone are attributed to the fact that there is an abrupt change to the plane of support for a workpiece when it passes from the hearth onto the inclined skids. At the transition area of support, the heated slag on the bottom of the workpiece is scraped loose and adheres to the hearth. As each workpiece slides over the adhered slag, more slag is released and adheres to the hearth. Some of the slag breaks loose causing the erratic movement of the workpieces. For example, a workpiece may slide down the skids upon an edge instead of its bottom surface. Thus, in order to avoid damage to the structure forming the reheat furnace, it is necessary to periodically remove adhered slag from the hearth in the workpiece drop-out zone as well as the other workpiece support surfaces throughout the furnace so as to assure proper movement of the workpieces through the furnace.
It is not practical or feasible to discontinue operation of the reheat furnace to carry out such cleaning operations because if the adhered slag is allowed to cool down to an ambient temperature, the slag becomes so hard that it is virtually impossible to break it loose without damaging the refractory material of the hearth. In this respect, the slag may take the form of iron silicate having a melting temperature of about 2200.degree. F and forms a very tight adhesive bond to the refractory material of the hearth.
In the past, it was proposed to clean slag from a furnace hearth by employing a cleaning slab such as disclosed in U.S. Pat. No. 2,132,591. The cleaning slab which took the form of an inverted U-shaped member, was placed on the entry table at the charging side of the furnace so that it was advanced through the furnace between two adjacent workpieces. As the cleaning slab passed over the hearth, it was intended that plow-like edges on legs of the cleaning slab would scrape along the top surface of the hearth to thereby loosen the accumulated slag or cinders which were then either removed through the side opening in the cleaning slab or carried through the furnace to the discharge side of the furnace.
The proposed use of such a cleaning slab has the apparent advantage that it eliminates downtime of the furnace because the cleaning operation is carried out while the furnace continues its normal operation. However, adhered slag cannot be effectively loosened for removal by the cleaning slab without first manually digging the slag loose. The cleaning slab suffers from certain other acute disadvantages which the present invention is designed to overcome. Specifically, for example, the apparatus of the present invention is designed for control by an operator so that the cleaning process is not dependent upon unpredictable movements of workpieces through the furnace. In this regard, should the cleaning slab "dig" into the slag at one side of the furnace but not the other side, then the cleaning slab may be expelled from its intended location between two adjacent workpieces under the developed or applied force by a pusher at one end of the furnace. Moreover, it is virtually impossible to control the depth of penetration by such a cleaning slab into the slag. Usually the slab simply rides or passes over the slag or other material that builds up on the hearth. It is a likely possibility that the cleaning slab will dig into the refractory material of the hearth and damage it while moving along the furnace.